1. Field of the Invention
The present invention relates to a hollow fiber apparatus for culturing cells and to a method of using the apparatus to grow and maintain living cells in vitro.
2. Description of the Prior Art
Various hollow fiber apparatus have been used to grow and maintain living cells in vitro. These apparatus typically include a hollow shell with a plurality of semi-porous hollow fiber membranes extending through shell. A fluid medium containing oxygen,nutrients and other chemical stimuli is circulated through the lumen of the hollow fiber membranes. Cells are seeded in an extracapillary fluid space between the fiber membranes and the shell wall. The oxygen, nutrients and other chemical stimuli diffuse through the semi-porous walls of the hollow fiber membranes into the extracapillary space to maintain and stimulate the growth of the cells. Simultaneously, waste products and contaminating proteins diffuse from the extracapillary space through the walls and into the lumen of the hollow fibers, and are carried away by the fluid medium. The cell culture device of U.S. Pat. No. 3,821,087 to Knazek et al. is representative of this type of cell culture device, and U.S. Pat. No. 3,883,393 to Knazek et al. and U.S. Pat. No. 4,391,912 to Yoshida et al. generally describe a method of using such an apparatus.
To economically produce cell derived products in a hollow fiber culture device, a large number of cells must be maintained viable in optimal culture conditions for product formation over long periods of time. Prior art hollow fiber culture devices, such as disclosed in U.S. Pat. No. 3,821,087 to Knazek et al., have many limitations that prevent their use in the economical production of cell derived products in commercial quantities. One limitation of these prior art hollow fiber culture devices is that the fibers frequently stick together and reduce the surface area to which the cells may attach. Also, the fibers are not equidistantly spaced in the cell culture device. As the cells grow and the cell density increases, it becomes more difficult for the nutrients, oxygen and other chemical stimuli to diffuse through the walls of the hollow fiber membranes and through the layers of cells that have developed to reach remote cells (cells which are the furthest away from the fiber membranes) and for waste material produced by the remote cells to diffuse back into the lumen of the hollow fiber membranes. This results in anoxic or dead spaces. Cells located within these spaces will die due to the lack of oxygen or failure of nutrients to reach the cells by diffusion.
Another limitation is that very little fluid motion occurs in the cell compartment. Limited fluid motion in the cell compartment (extracapillary space) leads to micro environments forming around quickly metabolizing cells, adversely affecting other cells in the cell culture apparatus by altering PH.
The present invention is designed to overcome these limitations.